The present invention relates to the production of monocarboxylic acids. More particularly, it relates to the continuous production of acetic and propionic acids by simultaneous carbonylation of methanol and ethylene, respectively, in a single reactor.
A process for producing carboxylic acids and esters or mixtures of these compounds specifically by the reaction of an alcohol, or the ester, ether and halide derivative thereof, with carbon monoxide in the presence of a catalyst system consisting essentially of a rhodium compound and a halogen component is described in U.S. Pat. No. 3,769,329. The method is particularly suitable for the production of acetic acid from methanol and carbon monoxide in the liquid phase. Propionic acid is one of the many products which can be made from ethylene by using the liquid-phase process described and claimed in U.S. Pat. No. 3,579,552. This patent relates to producing a carboxylic acid by reacting an ethylenically unsaturated feedstock of from 2 to 30 carbon atoms with carbon monoxide and water in contact with a rhodium compound and a halogen promoter as the catalyst system.
The fact that acetic acid and propionic acid can be produced continuously in a single reactor by simultaneous carbonylation of ethylene and methanol using the catalyst system disclosed in the above-mentioned patents is known from "Research Disclosure," Dec. 1974, No. 128, Page 18. It would be expected from this disclosure that the two carbonylations would proceed independently in the same reactor environment with no interaction or influence of one upon the other. Accordingly, a substantially larger reactor would be required for the production of a predetermined quantity of both acids simultaneously than would be required for the production of either acid separately. However, it has now been discovered unexpectedly that the rate of reaction for the production of propionic acid is improved when this acid is produced from ethylene along with acetic acid being produced from methanol at specified conditions over the rate which prevails under the same conditions when it is produced separately. This makes possible the production of both acids simultaneously in a single reactor of the same size as would normally be employed to produce comparable quantities of either product separately.